The Advanced Vitrification System is a “melt-in-the-final-disposal-container,” waste vitrification technology and method of in-situ vitrification of waste materials in a disposable canister. It is disclosed in U.S. Pat. No. 5,678,237, which is incorporated herein by reference. For purposes of this disclosure, the technology and method described in U.S. Pat. No. 5,678,237 is part of the technology and method referred to as AVS-1. For purposes of this disclosure, the AVS-1 also comprises the single walled crucible of U.S. Pat. No. 6,485,404. Also for purposes of this invention, the term “waste” includes the waste all the material requiring disposal and all additives with which such material is mixed to promote vitrification.
The disclosure of U.S. Pat. No. 6,558,308 issued 06 May 2003, which describes a heating methodology for the AVS-1, is incorporated herein by reference. The disclosure of U.S. Pat. No. 6,485,404 issued 26 Nov. 2002, which describes a single-walled crucible for the AVS-1, is incorporated herein by reference.
This invention is a modification of AVS-1 technology and method of vitrification and is referred to herein as the Advanced Vitrification System 2, or AVS-2. In the AVS-2, the final disposal container is made into “AVS-2 Melter Module,” which undergoes “multiple use” before it is filled and sealed for disposal. Essentially, to enable multiple use, a drain is added to the bottom of an AVS-1 module to enable molten waste to be drained into a standard canister. In contrast, the AVS-1 module had no bottom drain and the AVS-1 method anticipated a “single-use” or “single-cycle” for the vitrification process in the final disposal container.
Objects of the AVS-2 invention are: (1) to lower overall cost to permit competitive vitrification of a larger range of wastes, for example, high-level radioactive waste, low-level radioactive waste and hazardous waste. (2) to increase production rate of canisters of vitrified waste from a given size facility. (3) to increase the canister fill factor because of the canisters filled from the bottom drain need not have the AVS-1 module internals needed to melt the waste. Such a filled canister can be filled up to about 95% of the canister height. (4) to ease and simplify the disconnect/connect operations for feed and off-gas piping. Such operations need only be done for the AVS-2 when the AVS-2 Melter Module has concluded its operational lifetime. (5) to increase the cooling rate of the vitrified product, which improves its leach resistance. (6) to ease melter decontamination, decommissioning, and disposal, since the melter is the AVS-2 Melter Module and it can be disposed of in the same manner as a disposal canister. (7) to ease control of the in-can vitrification process, since the AVS-2 Melter Module can be run continuously at steady rate.
The Advanced Vitrification System (AVS-1)vitrifies waste directly inside the final disposal canister. In the art, the term “canister” and “container” are used interchangeably. Thus, the melter is also the disposal container or canister. When the waste is highly radioactive, toxic or hazardous, disposal of the waste and the melter together greatly simplifies the process from the current generation melter technology.
The primary method of heating the wastes in the disposal container is by energizing a surrounding induction coil, which heats the waste directly and indirectly through heated walls of the surrounding container. However, the means for heating may be other traditional means well known in the art: for example, by direct or indirect electric resistance or by adding radio frequency energy.
Direct vitrification in the final disposal canister made the AVS-1 completely different from the current generation melter technology used in the United States Department of Energy's (DOE) baseline melter program. In DOE's baseline melter program, radioactive waste is continuously fed into a large pot melter, generically known as a “pot melter,” or a “Joule-heated melter.” An electric current passes through the waste between two electrodes within the pot melter, melting the waste. The molten waste is then poured into a disposal canister.
The DOE's baseline program assumes that the pot melter will be re-used for several years and then disassembled and disposed of in accordance with the rules, a process generally known as decontamination and decommissioning (D&D). Two large uncertainties are: (1) how to D&D a joule melter, considering that the pot melter will be highly contaminated with high-level radioactive wastes: Development of the D&D process is left to the future; and (2) how to ensure pot melter lifetime with the unique prospect of widely varying waste chemistry.
An important benefit of the AVS-2 is that there is no contaminated melter equipment requiring special handling for decontamination, decommissioning and disposal. Overall, contamination concerns are significantly reduced because the entire melter system is isolated —no emissions into the cell —and the disconnects of the feed and off-gas pipes from the AVS-2 Melter Module are at minimum intervals of a month or two.
Thus, each AVS-2 Melter Module is re-used multiple times as a melter and then filled with vitrified waste, sealed-off and disposed of, greatly simplifying melter disposal.